The present disclosure generally relates to systems and methods for monitoring health of stationary blades or stator vanes.
A gas turbine may include an axial compressor at the front, one or more combustors around the middle, and a turbine at the rear. Typically, an axial compressor has a series of stages with each stage comprising a row of rotor blades or airfoils followed by a row of static blades or static airfoils. Accordingly, each stage comprises a pair of rotor blades or airfoils and static airfoils. Typically, the rotor blades or airfoils increase the kinetic energy of a fluid that enters the axial compressor through an inlet. Furthermore, the static blades or static airfoils generally convert the increased kinetic energy of the fluid into static pressure through diffusion. Accordingly, the rotor blades or airfoils and static airfoils play a vital role to increase the pressure of the fluid.
Furthermore, the rotor blades or airfoils and the static airfoils are vital due to wide and varied applications of the axial compressors that include the airfoils. Axial compressors, for example, may be used in a number of devices, such as, land based gas turbines, jet engines, high speed ship engines, small scale power stations, or the like. In addition, the axial compressors may be used in varied applications, such as, large volume air separation plants, blast furnace air, fluid catalytic cracking air, propane dehydrogenation, or the like.
Moisture/humidity, high temperatures etcetera in the environment lead to corrosion of various airfoils and other structures inside the gas turbine. This, in combination with low cycle fatigue and high cycle fatigue during operation of the turbine, lead to stress-corrosion cracking, especially, if extreme stress is experienced due to abnormal resonances or impact of foreign objects. Additionally, the airfoils operate for long hours under extreme and varied operating conditions such as, high speed, pressure and temperature that affect the health of the airfoils. In addition to the extreme and varied conditions, certain other factors lead to fatigue and stress of the airfoils. The factors, for example, may include inertial forces including centrifugal force, pressure, excitation of the resonant frequencies of the airfoils, vibrations in the airfoils, vibratory stresses, temperature stresses, reseating of the airfoils, load of the gas or other fluid, or the like. A prolonged increase in stress and fatigue over a period of time leads to defects and cracks in the airfoils. One or more of the cracks may widen with time to result in liberation of an airfoil or a portion of the airfoil. The liberation of airfoil may be hazardous for the device that includes the airfoils, and thus may lead to enormous monetary losses. In addition, it may create an unsafe environment for people near the device and result in serious injuries.
Conventional systems and methods exist to monitor the performance and operation of compressors and the airfoils. For example, vibration sensors may be used to monitor vibrations from the compressors and the airfoils during operations. A change in the frequency or magnitude of existing vibrations may indicate excessive wear and/or crack formation. However, vibration sensors may only detect cracks and other anomalies that are large enough to cause an imbalance and vibration in the compressor. As a result, vibration sensors may not detect small cracks that do not result in a detectable vibration in the stator vanes. Accordingly, it is highly desirable to develop the present systems and methods that monitor the health of the airfoils.